Steering devices are provided at the rear side of marine vehicles such as vessels to change the direction of movement both in forward and backward directions while maneuvering, such devices consist mainly of an arm, a shaft, and a rudder
In a typical shaft-rudder construction, vertical axis of the rudder shaft becomes positioned on the front of the rudder when the marine vehicle moves forward, and since the area on the rudder's front section that is exposed to water load during forward motion is relatively small, the rudder can be easily controlled. In other words, since no rudder area is left on the front of the rudder shaft while moving forward, water cannot exert force on such ‘non-present’ area, which provides an easy control of steering attempts of the vessel.
The preceding condition, however, is much different as such vessel moves backward. In other words, the vertical axis of the rudder shaft becomes positioned on the rear with respect to the rudder's surface area, exposing the rudder's area to water load when the vessel moves backward, and making difficult to control the rudder and exposing the mechanical components thereof to external forces.